To see what events your local store has available, and that you can check into please log into the Fleet Feet app. Click on the calendar icon with the word "Events" below it, which is located in the bottom right hand side of the app. Then click on the "Available" section.
Here you will see events you can check into. To check in, simply click on the event you would like to attend (on the day of, and close to the time the event starts), and press the orange "Check In" button. This will check you into the event, and add miles to your account if it was advertised with miles.